Mercaptalation of sugar



patented Aug. 14, 1 951 MERCAPTALATION OF SUGAR James Masanobu Sugihara, Salt Lake City, Utah, assignor to Sugar Research Foundation, Inc., New York, N. Y., a corporation of New York No Drawing. Application May 24, 1947, Serial No. 750,375

5 Claims. 1

This invention relates to the catalytic mercaptalationof sugars. More particularly, my invention relates to the mercaptalation of sugar liquors containing sucrose and to a novel means for utilizing the fructose remaining after the mercaptalation.

Sucrose is a polysaccharide resulting from the condensation of a molecule of dextrose with a molecule of fructose. Since the acid hydrolysis of sucrose results in the ready production of almost quantitative yields of equal amounts of dextrose and fructose, sucrose may be considered to be a cheap source for these two reducing sugars. In spite of this fact, the problem .of profitably utilizing the dextrose and fructose available from sucrose has hitherto been a difficult one. This is due to the excessive solubility of fructose in water, and to the difliculty and expense involved in obtaining reasonable yields of both of these sugars in crystalline form from inverted sucrose.

A successful means for utilizing both the dextrose and the fructose available in sucrose would be of considerable commercial importance not only from the standpoint of increased markets for pure crystalline sucrose, but particularly from the standpoint of utilizing the sucrose present in raw or spent commercial sugar liquors, such as sugar cane juice or beet sugar molasses. It has been found that the dextrose and fructose available from pure or crude sucrose liquors may both be profitably utilized by means of direct sucrose liquor mercaptalation followed by the conversion of the non-mercaptalated fructose to levulinic acid.

Accordingly, one of the objects of this invene or spent sucrose liquors or from cane or beet sugar juices.

A further object of my invention is to provide a process which enables the direct production of glucose mercaptals from raw or spent sucrose liquors or juices, and which enables the production of levulinic acid from the crude fructose left after the mercaptalation of the crude sugar liquors.

Still another object is to provide an improved sugar mercaptalation process which enables optimum glucose mercaptal yields with lower alkyl mercaptans.

I have discovered that polysaccharides which yield aldose on splitting do not have to be subjected to a previous splitting before mercaptalating the aldose.

I have also discovered that polysaccharides whose molecules consist of condensation products of aldoses and ketoses may have their aldoses mercaptalated without any accompanying ketose mercaptalation by subjecting such polysaccharides to direct mercaptalation in the presence of mineral acid catalysts.

It has been found that when aqueous sucrose solutions are mercaptalated in the presence of mineral acid or acid salt catalysts, a simultaneous sucrose splitting and mercaptalation takes place with the simultaneous production of glucose mercaptal and free fructose. Such mercaptalations readily take place with lower primary mercaptans.

With higher molecular weight mercaptans, such as lauryl mercaptan, the reaction is minor, and in the case of lower secondary or tertiary triercaptans, little or no reaction takes place. Mercaptalation with lower primary mercaptans may be readily carried out not only with sucrose, but with other aldose-containing polysaccharides,

such as maltose, starch, or dextrins.

After discovering that it was possible to obtain glucose mercaptal in good yield by the direct mercaptalation of pure sucrose, attempts were armed to directly mercaptalate crude sugar. liquors, such as molasses, and low-grade raw beet sugar liquors. Since these liquors consists of numerous and complex impurities, it was expected that. the mercaptalation of the sucrose in these crude liquors would result in considerably lower yields than those obtained when starting with pure sucrose. Actual tests, however, led to the unexpected discovery that it is possible to obtain substantially the same yields of glucose mercaptal with crude sugar liquors as those obtained when starting with pure sucrose. This discovery is of practical commercial significance, since it enables optimum yields for individual glucose mercaptals.

In working with themethyl, ethyl, n-propyl, and n-butyl mercaptans, Ighave found that the best conditions of such variables as temperature, time,

acid strength, and acid volume vary with each 5 Hydrochloric acid is the best glucose mercaptal. catalyst from the standpoint of yieldsand general-workability. In going from methylto-butyl glucose mercaptals, the general trend with increasing mercaptan molecular weight',- for .opti

mum yields, is increased hydrochloric acid concentration as well as acid volume. It has been I discovered that best yields for the individual methyl, ethyl, n-propyl, and n-butyl glucose mercaptals are obtained when the concentration of thehydrochloric acid catalysts is about ,8, 9, ,10, and 11 molar, respectively. It has also been found that best yields with these molar .acid concentrations are obtained when one mole of sucrose is dissolved in about 0.3liter of acid soluticncontaining about 2.3 moles of hydrochloric acid in the case of methyl mercaptan. When working with ethyl mercaptan, best results occur whenarnole of sucrose is dissolved in about 0.4 liter of acid containing 3.5 moles of hydrochloric acid. In the case of n-propyl mercaptan, the best results are obtained when a 'moleof sucrose is dissolved in 0.68 literof acid containing 6.8 moles of hydrochloric acid. With n-butyl mercaptan, best resultsare obtained when a mole of .sucrose is dissolved in 0.65 liter of acid containing 7.1 moles of hydrochloric acid;

, The volume of hydrochloricacid used is animp'ortant variable. When the volume is too small,

in order that the volume of acidified molasses should not be increased to such an extent ,that mercaptal yields will be deleteriously affected.

Having now indicated in a general way the nature and purpose of this invention, there follows a more detailed description of the invention in the form of examples.

EXAMPLE i Glucose dimethyl mercaptal from sucrose 35.5 grams (0.104 mole.) ofpuresucrose were. dissolved-in cc.-of-8 M hydrochloric acid, and the resultingacidified sugar solution transferred to a reaction flask. The mixture was cooled .to 5 C., andlO grams (0.208; mole) ;ofmethylmercaptan added. The reaction medium was -vigorus y st ed o ab ut 15 minut s while bein maintained at 5 C. The reaction flask was then maintained at about 0 C. for about 5 hours. There resulted a solid cake consisting substantially of a mixture of mercaptal, fructose, and aqueous hydrochloric acid. The solid cake was broken up, mixed with about 25 cc. of ice water, and transferred to a suction filter. The filter cake, consisting of crude mercaptal, was removed from the filter, suspended in about 25 cc. of ice water, and re-filtered. The filter cake was washed until the hydrochloric acid and fructose were removed. The resulting crude lglucose dimethyl mercaptal was re-crystallized from hot water, filtered, and dried. There was obtained 12 vgrams of mercaptal, representing about 45 per cent of theoretical yield,

The yield:of.glucose dimethyl mercaptal is sig nificantly affected by hydrochloric acid volume and concentration. 'With '7, 8, and 9 molar acid concentrations, theyields were 12, 45, and 19 per cent, respectively, all 'other conditions being equal. *When the ratio of weight of sucrose in gram-s te cc. of 8 M hydrochloric acid is 1 to 0.85, maximumv yields are obtained. When the ratio is 1 to 0.99, somewhat lower yields result; and

mole) of sucrose. The solution was cooled by means of an ice bathto 0C.,and thereafter '78 cc.

(1 mole) ethyl mercaptan was added. The. con-' tents were vigorously stirred while maintaining the reaction medium at 0 C. until solidification began. The semi-solid material was transferred into a 600 cc. beakerat 0 C.. for aboutd hours. The resulting solid cake, consisting of a mixture of mercaptal, fructose,. and hydrochloric acid so.- lution, was transferred to asuction filter with .a minimum amount of ice water. The filter cake was brokenup and suspendeddn. sufficient ice water to obtain a mushy suspension. .Washingand filtering were repeated .at least three times, or until only traces cf hydrochloric acid remained. The finalfilter .cake .is preferably washed with a smallamount of diethyl ether .to remove substances which tend to .discolor the product .as well as any unreacted .mercaptan. The washed filter cake was then air-dried. There was obtained l00 gramsofwhite, stable, dry glucose di ethyl mercaptal, whichrepresents abouta 70,.per cent yieldf Yields are-affectedby acid ,concentration and volume. .At..10 M. the yield is aboutfil per cent. At a sucrose-9M acid ratioof'between about 1 to 1.1 and 1 to 1.3, optimum yields of about to percent -.ar.e obtained. Ata ratioof .1 to 0.93, the yield is .about39 percent, and at a ratio of .1 to 1.4, theyield is about A9,.per cent.

EXAMPLE III Glucose dz'propyl mercaptcl from sucrose 171 grams :(05 mole) -of sucrose :were dissolved in 335 cc. of 10 M. hydrochloric acid in a liter flask. The:resultingsolutionwas cooled intan ice bath. There ,was thenrapidlyadded 94.4 cc. .:of npropyl mercaptan, and the resulting reaction medium was vigorously stirred until the extent of solid formation prevented .further mixing. During this :time the a batch was maintained :at

- 0 -;C. This pe1: ation requires about 40 minutes.

The resulting solid mass was transferred to a 600 cc. beaker and maintained at about C. for about hours. sisting of mercaptal, fructose, and hydrochloric acid solution, was broken up and transferred to a suction filter with a minimum of ice water. The.

pressed filter cake was then broken up and resuspended in ice water. The mercaptal was then filtered, and this operation of filtering and resuspension in ice water repeated until substantially all of the hydrochloric acid had been removed. The washed mercaptal filter cake was then given a final wash of diethyl ether to remove the light yellow color which contaminated the product. The filter cake was air-dried, and the dry product, consisting of glucose dipropyl mercaptal, weighed 120 grams, representing about a 76 per cent yield.

With 11 M acid, under the same conditions, the yield was 71 per cent. At a sucrose- M acid gram to cc. ratio of between 1 to 1.8 and 1 to 2.1, yields of about 76 to 78 per cent are obtained.

EXAMPLE IV Glucose dibutyl mercaptal from sucrose 171 grams (0.5 mole) of sucrose were dissolved in 336 cc. of 11 M hydrochloric acid in a liter flask. The resulting solution was cooled in an ice bath. There was then rapidly added 127 cc. of 85 per cent n-butyl mercaptan. The mixture was then subjected to the same treatment as that described in Example III. There was obtained 130 grams of dry glucose dibutyl mercaptal, representing a 76 per cent yield.

With 12 M acid, the yield is about 63 per cent. Best yields are obtained when the sucrose-acid gram to cc. ratio is between 1 to 1.4 and 1 to 2.3.

EXAMPLE V Glucose dibutyl mercaptal from cane molasses Ordinary cane molasses contains between 33 and 38 per cent sucrose, and between about 16 and 21 per cent invert sugar, the total sugar in the molasses ranging between about 50 and 60 per cent. A sufficient volume of cane molasses analyzing 52 per cent total sugar was measured so as to be equivalent to 30 grams of sugar dry substance. This cane molasses was mercaptalated with cc. of n-butyl mercaptan in the presence of 50 cc. of 11 M hydrochloric acid at 0 C. under the same conditions as that described in Example IV. The 50 cc. of 11 M hydrochloric acid represents the total aqueous volume of the reaction mixture, and includes the water in the original molasses. By knowing the water content of the molasses, one may calculate the correct Volume and strength of aqueous acid necessary to make a total volume of 50 cc. 11 M solution. This is best accomplished when a part of the hydrochloric acid is added to the reaction mixture in the gaseous form. It is preferable to first dilute the molasses with concentrated hydrochloric acid solution and then bring the reaction mixture up to 11 molar strength by the addition of hydrogen chloride gas.

The mercaptalation was carried out under the same conditions as that described in Example IV. There was obtained 18.2 grams of glucose dibutyl mercaptal, representing a 67 per cent yield. This compares with a 74 per cent yield when starting with pure sucrose.

Better results are obtained with molasses when a part of the acid is added in gaseous form. This permits a regulation of the total concentration The resultant hard cake, con-.

Glucose diethyl mercaptal from various sucrose of acid as well as the total aqueous volume. The.

addition of a small volume of aqueous acid prior to the gaseous hydrogen chloride increases the fluidity of the viscous molasses and makes ready mixing possible with the mercaptan. Excessive viscosity of the reaction mixture also makes subsequent mercaptal filteration impractical.

EXAMPLE VI Glucose dibutyl mercaptal from other sucrose sources In Table 1, shown below, there are submitted the results obtained when various sucrose materials were subjected to n-butyl mercaptan treatment by the same method described in Example V;

TABLE 1 [30 grams sugar+20 cc. n-buty1 Bigeecaptan+50 cc. 11 M HCl mixed at in the combined form of 9 molar solution and gaseous hydrochloride in order that the optimum volume of 9 M hydrochloric acid be obtained for best mercaptal yields. The reasons for the use of gaseous hydrogen chloride have been given in Example V.

TABLE 2 [171 grams sucrose-[-78 cc. ethyl mercaptan+u M HCl mixed at 0 (1.]

Mixing Per Source of Sugar Time 33 Grams of Cent HCl (Minutes) at O O. Mercsptal Yield Sucrose 183 33 5 98 69 .Brown Cane 183 44 4 88 62 Sucrose 220 32 5 67 Brown Cane Sugaiz. 220 65 4 9 67 "Intermediate Raws. 183 38 6 70 Lowgrade RawsL 183 42 5 5 82 57 The above tables illustrate the unexpectedly good yields obtained with molasses and crude sugars as compared to yields obtained with pure sucrose when operating at 0 0. Similar results are obtained when mercaptalating at 20 C. Between zero and 20 0., optimum yields are obtained. Above or below this range, the yields are materially lowered. Similar comparative results may be obtained when using either methyl or propyl meroaptan.

The intermediate raws and the low-grade raws referred to in Tables 1 and 2 are secondary products formed during the production of sugar from beets. They are usually purified by returning to an earlier stage of the processing. In

place of the commercial cane or beet molasses essence:

ref erred it) :in the-tables; one may,:use.:-.dehydratedf:

molasses: and obtain: similar. results. 1

EXAMBLE viIIIi Lewmnic acid; fromglucose. mercaptcli filtrates...

The-fructose filtrates obtained in theprepara tion of the glucose" mercapta-ls of Examples I= through VII were combinedand a portion of 1.5 liters of the combined filtrate containing about 1.5 moles of fructose was. used for levulinic-acid production. To this liquor there was added 100 cc. of concentrated. hydrochloric. acid, which made the acidconcentration of the acidified mix-.-

ture about 6 molar. The acidified fructosesolue tion. was then heatedata simmer for 3. hours and then placed on a boiling-water bath for 42 hours. The black solid which formed was removed by filtration and washed with water. Thewashings were added to the filtrate, and the latter then evaporated nearly to dryness. The resulting mixture of black liquor and solids was extracted with ethyl ether for 48 hours and then filtered; The ether was then removed by evaporation and the remaining black solution vac-- Hum-distilled. The distillate boiling between 130 and 190 C. was recovered and re-distilled at re- 7 subjectingthese filtrates to a levulinic acid con-.

v rsion un er super mosph ric Pressure 0011:- ditions. The mercaptal filtrate need notnecesr sarily be a combined filtrate from. two or more, mercaptalations with different mercaptans, but can oi' urs be fi trat ntaining fruct se. andoriginating from an individualjmercaptalation, such as, for ins ance, the filtrate. obtained fromv glucose dibutyl mercaptal'.

Although my preferred 'mercaptalating, (iota-- lyst ishydroc'hloric acid, one may, if one desires, use other acid or acid salt catalysts. The. acid preferably should be one which brings about aldose mercaptalation without any deleterious efiects on sucrose or fructose. The choice of mercaptan depends upon the type of mercaptal sought. and on-;the,commercial availability of the mercaptan. Any mercapt'an capable of reacting with the aldehydic group of an aldose may be used, preferably a mercaptan having no destruc: ti've effect on sucrose or fructose. Thus, alkylenemercaptans, such as ethylene or butylene primary. mercaptans may be used.

Although preferred methods of operating my invention have been given, many variations in proced -ire1 or in. the; material processed: will. be

describedprocedure as herein taught-norbythe xample g ven, but isto be limitedzonlyas'set.

forth. in. the; accompanying; claims forming a part. of: this.:$t ecification.

I claim:

1. A process for obtaining glucose: .dimcthyl mercaptal which com-prises; dissolving. sucrose in aboutzdmoiar aqueous hydrochloric acid, cool;

ing; the; acid; sucrose solution to about: .Q C.,'

adding-r methyl: merca-ptan, mercaptalating the sugarzsolutioniataabout *5 C: with simultaneous agitation. of; the reaction medium. for about one,

hour,- maintaining the reaction medium quies... cent at about: 0": C; for: substantially. five hours whereby: a: solid: cake. of crude glucose dimethyl'; mercaptal' is. produced; disintegrating and. sus. pendin said= cake: in ice water, filtering and-: washing with ice water until substantiallyall of: the excess hydrochloric-acid is removed; re. dissolving the washed cake in hot Waterand re-crystallizing theglucose dimethyl mercaptal;

2; Process'ior the produetion of glucose diethy-l mercapta-l which com-prises dissolving a sucrose in about 9- molar; aqueous hydroehloriofacidcata lyst; cooling theacid sucrose solution to about 0 (3:; adding ethylmercaptan andmercaptalating the sugar solution atabout 0 C. with simule taneo s. aeita onci the. rcactionmedium; subsequently maintaining the reaction medium, quiescent. atabout. 0f ior abouti'our hour whereby. asubstantially solidcake of crude'glue. oseiethyl mercaptal' is ob ain d; disinteg ate irlg, said cake and suspending i'tfin ice wat rs! filtering the suspension; washing the filter cake with ice Water until substantially all of the acid s er m v r; andums; he was ed-sl cose diethyl mercaptal filter cake.

3, Process, for the production of glucose. dipropyl mercaptal= which comprises: dissolving; sucrose in about 1.0"m0l'ar aqueous hydrochloric a id. c y t; oo ing. h a i su rose solut on;

to about. 0 adding .nrprop l. mercaptan, and; mercaptalating, the. su ar.- solution at about. 03 0-. w h. simult neous a i a ion of he. reaction. medium; subsequently. maintaining the reactionmedium quiescentat abputO C. foraboutfour hourswhereby. a substantiallysolid cake-.o f-crude glucose di ropyl m rcantalds; formed; is ntergrating said cake and suspending it in ice water; filtering the suspension; washing the filter cake with ice.- water; until: substantially all of the-acid catalyst is removed; and drying the washeglglucosedipropyl mercap ta-l filter cake.

Process for the production of. lu os di: butyl mercaptalwhich comprises; dissolving. su,- crose in about 11.molaraqueoushydr hl ric.acid. cat lyst; cooling. the acid sucrose solution; t o C. adding. nebuty mcrcantan ndme 'e aptalatin th su ar. ution at about. 0? with tancous gitatiofi oft e reaction me um;subsequentl maint in ng h rcaction me uniuuiescent at about-1). C. for about. fo rhou a whereby a-substantially. solidcake of; or deglu cose dihutylz mercantal. isI formed; d= me; aid ake nd usiqen in it; water;- lfli t suspension; washin the; filtercaha with iccwater-until.substantiallyrall-.oftheacidz talyst isremoved; :nd:.dryi-ngi.the washed glue cosedibutyl mercaptalfilteroake.

5..A-., process. forspobtaining: a glucose dialkylmercaptal which comprises.dissolvingsucrose in aboutrfrom' 8; to 11 molar aqueous:hydrochloric acid, cooling the resultant acidsucrose 1 solution I to. about =59 CJ, adding an alkyl mercaptan; mercaptalatingthe= resulting sugar solution at about 5 C. with simultaneous agitation of-the reaction medium- -for about one hour; maintaining" thereaction medium quiescent at about-0? C; for substantially' -fi've hourswhereby a solid-- cake of I a crude glucose dialkyl mercaptal is produced; disintegratingand suspendin said'c ake in ice water, filtering and washing with ice-wateruntil substantiallyall ofthe excess hydrochloric acidand" soluble material is removed; then. dis? solving thethuswashed cake in hot water and 10 recrystallizing therefrom the formed glucose (11- OTHER REFERENCES alkyl mercaptal. B 2 13 4 0 6 J s MASANOBU SUG A palgieher. erichte, v 7 9 DD 7 679, '7 Uyeda et aL: Bull. Chem. Soc., Japan, v. 1 REFERENCES CITED 5 (1926), pp. 179-182, 4 pp.; v. 4 (1929). pp. 264- The following references are of record in the 265,2 pp. file of h s pa Wolfrom et aL: JACS, v01. 56 (1934), pp. 880- UNITED STATES PATENTS 881, 2 pages; V01. 61 (1939), pp. 1072, 2172, 2 Number Name Date 10 pages; vol. 63 (1941), p. 1338, 1 page, v01. 65

1895 41 4 Helwig Jam 24' 1933 1522 p. 2 1 a 67 (1945), on 500-501, 2,295,760 Sohreiber Sept. 15, 1942 

5. A PROCESS FOR OBTAINING A GLUCOSE DIALKYL MERCAPTAL WHICH COMPRISES DISSOLVING SUCROSE IN ABOUT FROM 8 TO 11 MOLAR AQUEOUS HYDROCHLORIC ACID, COOLING THE RESULTANT ACID SUCROSE SOLUTION TO ABOUT -5* C. ADDING AN ALKYL MERCAPTAN, MERCAPTALATING THE RESULTING SUGAR SOLUTION AT ABOUT -5* C. WITH SIMULTANEOUS AGITATION OF THE REACTION MEDIUM FOR ABOUT ONE HOUR, MAINTAINING THE REACTION MEDIUM QUIESCENT AT ABOUT 0* C. FOR SUBSTANTIALLY FIVE HOURS WHEREBY A SOLID CAKE OF A CRUDE GLUOCOSE DIALKYL MERCAPTAL IS PRODUCED, DISINTERGRATING AND SUSPENDING SAID CAKE IN ICE WATER, FILTERING AND WASHING WITH ICE WATER UNTIL SUBSTANTIALLY ALL OF THE EXCESS HYDROCHLORIC ACID AND SOLUBLE MATERIAL IS REMOVED, THEN DISSOLVING THE THUS WASHED CAKE IN HOT WATER AND RECRYSTALLIZING THEREFROM THE FORMED GLUCOSE DIALKYL MERCAPTAL. 